T cells play an important role in protective adaptive immune responses, but also contribute to inflammatory diseases such as rheumatoid arthritis, Type I diabetes mellitus, and graft rejection. They elicit a wide range of effector activities by secreting various cytokines and cytotoxic factors that influence other immune cells and surrounding tissue. However, gaps remain in our understanding of the shared common pathways that lead up to their release. Classically, secreted proteins travel from the endoplasmic reticulum (ER) to the Golgi apparatus in vesicles generated by a group of proteins called Coat Protein Complex II (COPII). While COPII vesicles play a critical role in ER-to-Golgi transport, the processes driven by COPII vesicles in T cell functions such as effector cytokine release are unknown. The overall goal of this proposal is to study the role of COPII vesicles in T cell biology, and to examine their relevance in pathogenic and protective T cell processes in vivo. Given the fundamental role of COPII vesicles in the secretory pathway, the central hypothesis of this proposal is that the disruption of COPII vesicle formation will lead to defects in the release of specific cytokines by T cells and thus impact their biological functions. This hypothesis was formed based on preliminary data I have generated using novel T cell-specific conditional knock-out mice lacking a necessary component of the COPII coat, Sec23. The scientific aims of the proposal are: (1) to determine the impact of disruption of COPII formation on mature nave T cell functions, and (2) to determine the mechanisms of Sec23 paralogs in T cell functions. Under the first aim, I will explore the consequences of abrogating COPII formation on T cell protective and pathogenic functions. To do this, I will use well-established in vivo models of T cell-mediated anti-viral responses and alloimmunity, as well as explore relevance to human T cells. Under the second aim, I will explore whether T cells depend on different COPII paralogs for unique functions. Humans and mice carry two Sec23 paralogs, and it is believed that they can functionally compensate for each other and are expressed in a tissue-specific manner due to evolutionary shifts in gene expression. However, my preliminary data show the surprising observation that murine T cells express both paralogs. I will assess the contribution of these two Sec23 paralogs to broad cytokine secretion patterns using modern approaches to protein quantification and begin to explore the mechanisms of COPII-mediated transport in T cells. This proposal, when completed, will provide novel and fundamental insights into T cell-mediated immunity. It will also serve as a platform to achieve my training goals in experimental immunology, and to provide me with requisite training for my long- term goals as a physician scientist.